lt is well known that antibodies to pneumococcal capsular polysaccharides can he highly protective against pneumococcal infections. Unfortunately, these polysaccharides arc not immunogenic in young children and vaccines composed of them are not able to elicit protection until children have passed the age where they are at highest risk of pneumococcal infection. Recently however, data have been obtained that certain antibodies to teichoic acids and pneumococcal surface protein A (PspA) can be protective. Genetic analysis demonstrated that PspA is a virulence factor in pneumococci. My studies with PspA led to an observation on which the present grant application is based. Immunization of XID mice with adjuvant containing cell wall extract (CWE) from a rough pneumococcal strain in which we had inactivated the pspA gene, protected those mice with subsequent infection with pneumococci. This result indicated that there are other antigens in pneumococci in addition to the capsule, phosphocholine and PspA that can elicit protection. Since we used XID mice, it is unlikely that the antigen was the pneumococcal teichoic acids since XID mice do not make protective antibodies to this antigen or to most other polysaccharides. Pretreating the CWE with pronase or chloroform- butanol extracting prior to immunization eliminated its ability to elicit protection, thus indicating that the protective molecule(s) in the CWE is protein. My goal, in this study, is to identify and characterize the protection eliciting non-PspA pneumococcal surface protein(s), examine its strain distribution and assess its potential for use as a vaccinogen.